The disclosure relates generally to power systems and methods that employ generators for backup power to a facility, and more particularly, to a system, method, and controller for cooling a backup generator after use.
Typically, electrical power is provided from a primary source (such as a utility or a “grid”) to facilities that include residential, small business, and industrial environments. However, occasionally the electrical power is interrupted for reasons that may include weather damage to power lines and equipment, power plant shutdowns (scheduled or not), and other sorts of system failures such as cascading plant failures. Although the grid can be generally stable over time and may operate uninterrupted for months or more, the possibility of lost power from the primary source is nevertheless ever-present and can result in a range of hardships that extend from a inconvenience, to lost business, to life-threatening situations.
For instance, in a residential application, not only are the occupants inconvenienced, but if sump pumps, refrigerators, furnaces, and air conditioning units are not powered, this can lead to flooding in the basement, food spoilage, high temperatures within the residence during summer (e.g., stagnant hot temperatures), or dangerously low temperatures during the winter (e.g., for certain medical conditions, threat of burst water lines, risk of frostbite). A business as well, such as a restaurant, may experience food spoilage and customer dissatisfaction in the event of a power outage. In an industrial setting, if power is lost, a plant shutdown may occur that can lead to lost production and employee/equipment downtime, and some industrial facilities have a critical requirement for continuous power (such as certain plant processes, computer installations, and the like), such as a wastewater treatment plant in which a power loss can lead to overflowing tanks and untreated sewage discharge. Also, some facilities such as urgent care providers and hospitals rely on uninterrupted power to power life-supporting equipment. In many instances there is a legal requirement to provide uninterrupted, or minimally interrupted, power to the facility to avoid the repercussions that can occur if primary power is lost.
In some instances a battery backup is adequate to provide backup power. However, if no battery recharge capability is provided, then the battery can only provide backup until the batteries are depleted. Battery backup, as well, can be inconvenient to work and typically includes an inverter to generate AC power from the DC power of the battery. Such systems can therefore be costly, inconvenient, and may only provide a limited amount of backup capacity when primary power is lost.
As such, backup electrical generators are often provided that serve as a standby or secondary source in the event of primary power outage. The backup generator may be manually connected to loads within the facility when primary power is lost. Or, in many instances a backup system includes an automatic transfer switch (ATS) that detects power from the primary source, and when primary power is lost, the ATS controllably disconnects the primary source, powers up the standby generator, and engages the generator power with the loads. The ATS can work in reverse as well, so that when primary power is again online the ATS switches back to the primary and powers down the standby generator.
ATS' often have built-in time delays that are implemented during operation to ensure the least amount of interruption to the end user. In one example, there may be a time delay to allow automatic reclosers to occur before the ATS starts the generator, which protects against un-needed engine starts. Another example of a time delay is the time delay before transferring to the generator once the generator is running, which allows for proper engine warm-up before applying a load to it. And, another time delay is the time that the generator runs after it has been determined to shut down the generator and after the generator load has been removed (that is, to run in an unloaded state and cool the generator). ATS' typically have timers that are either hard coded and cannot be changed, dip switches that allow minimal choices in the time delay, or the time delay may be programmed in advance.
In one known design, a thermal sensor is used to detect when the generator has adequately cooled, and then shutdown occurs when the cooled temperature is reached. Thermal sensors, however, are prone to failure and add cost to the overall product, and may be located a distance from the generator itself (typically resulting in a long control line between the generator and the controller).
Thus, in a system with no thermal sensor, when the generator runs, whether due to 1) periodic running to exercise the generator/system, due to 2) a trigger that caused the generator to power up (such as a brief loss of primary power, but primary power is restored before loads are switched to the generator) or due to 3) an extended power outage, the timer counts down a predetermined amount of time to ensure that the engine is properly cooled. That is, regardless of the reason for generator operation or the duration and loads that have been placed on the generator, the unloaded runtime for the generator to allow cool down is the same. Such operation can lead to unnecessary extended runtimes, resulting in excessive fuel cost and needless engine wear.
Therefore, it is desirable to control the amount of engine cool down time to reduce fuel cost and reduce engine wear.